The effects of intra- and extra-erythrocytic factors upon the sickling propensity of SS erythrocytes and upon the deformability characteristics of normal and S erythrocytes will be characterized in these studies. These Studies are designed to clarify the effects of humoral substances which potentially enhance sickling directly, to study the indirect effects of environmental influences upon SS red cell function and behavior and to study the total red cell effects of antisickling agents such as cyanate.